1. Field of the Invention
The invention relates to a device for polarization-maintaining transmission of optical signals between units that are rotatable relative to each other. This is intended preferably for simultaneous transmission of a plurality of optical signals along a plurality of channels.
2. Description of Relevant Art
High bit-rate transmission systems having data rates of 80 Gbit/s and higher preferably perform transmission of optical signals in a polarization-maintaining manner. Here light is transmitted at a defined linear polarization. Polarized light is also employed with various optical sensors. Thus, a change of the polarization of the light can be evaluated by means of measured parameters. Optical signals of this kind must frequently be transmitted between units that are rotatable relative to each other.
Various transmission systems are known for basic transmission of optical signals between units that are rotatable relative to each other.
U.S. Pat. No. 5,568,578 discloses an optical rotating data transmission device for a plurality of channels, the device including a Dove prism. The polarization of coupled-in light changes with a rotation of the two units relative to each other. Furthermore, no transmission of light is possible at constant polarization even with employed components such as light-guiding fibers or collimators.
EP 1476969 discloses a rotating data transmission device in which the light is transmitted by multiple reflections in mirror-coated trench. The polarization of the incident light is changed in an unpredictable manner by the number of reflections which varies according to position.
US 2007/0237528 A1 discloses a polarization maintaining optical Rotary coupling. Linear polarized light is converted into circular polarized light for transmission between the rotating parts. Polarization converters are held by retainers resulting in a fragile assembly. Furthermore the surfaces of the polarization converters to surrounding air cause reflections of light therefore reducing return loss.